Controller and system for utility vehicle

ABSTRACT

A vehicle includes a pump having a swash plate tiltable about a swashplate tilt axis, wherein rotation of the swashplate changes the title angle and effects a change in volumetric displacement of the pump. A controller is operatively coupled to the swashplate to effect rotation of the swashplate, the controller including a processor and memory, and logic stored in the memory and executable by the processor, the logic configured to automatically control at least one vehicle characteristic independent of a user input command.

RELATED APPLICATION DATA

This application claims priority of U.S. Provisional Application No.61/985,604 filed on Apr. 29, 2014, which is incorporated herein byreference in its entirety.

FIELD OF THE INVENTION

The present invention relates generally to hydrostatic transmissions,and more particularly to control systems for hydrostatic transmissions.

BACKGROUND

Hydrostatic transmissions are well known and generally include ahydraulic pump and a hydraulic motor. The hydraulic pump and thehydraulic motor may be arranged as separate components or may becombined together in an integral unit. Axial swashplate type hydraulicpiston pumps are frequently used in many such hydrostatic transmissions.Such pumps generate a pump action by causing pistons to reciprocatewithin a piston bore, with reciprocation of the pistons being caused bya swashplate that the pistons act against as a cylinder barrelcontaining the pistons rotates. Pump fluid output flow or displacementfor each revolution of the barrel depends on the bore size and thepiston stroke as well as the number of pistons that are utilized. Theswashplate can pivot about a swashplate pivot center or axis, and theswashplate pivot angle determines the length of the piston stroke. Bychanging the swashplate angle, the pump displacement can be changed asis known in the art.

With the swashplate at its extreme pivot angle relative to the axis ofrotation of the barrel, a maximum fluid displacement is achieved. Whenthe swashplate is centered at a right angle relative to the axis ofrotation of the barrel, the pistons will not reciprocate and thedisplacement of the pump will be substantially zero. In some axialswashplate type piston pump designs, the swashplate has the capabilityof crossing over center which results in the pump displacement beinggenerated at opposite ports. In an over center swashplate axial pistonpump, each system port can be either an inlet or an outlet portdepending on the pivot angle of the swashplate. Over center axialswashplate piston pumps are widely used in hydrostatic transmissions, toprovide driving in both forward and reverse directions.

One use for hydrostatic transmissions is zero turn vehicles such as zeroturn lawn mowers. A separate over center swashplate axial piston pumpmay drive a hydraulic motor and wheel on each side of the vehicle. Whenthe swash plate angles of the two pumps are equal and the output flowrotates the wheels in the same direction at the same speed, the vehicletravels in a substantially straight line path in either the forward orthe reverse direction. When the swash plate angles of the two pumps arenot equal and the output flow rotates the wheels in the same directionbut at different speeds, the output flow rotates one wheel faster thanthe other so that the vehicle will turn. When one of the pumps isrotating its associated wheel in one direction and the other pump isrotating its associated wheel in the other direction, the vehicle willmake a zero radius turn. An operator interface allows the vehicleoperator to control the swashplate angles of the separate over centerswashplate axial piston pumps, to control straight line or turning orzero radius turns for the vehicle.

SUMMARY OF INVENTION

The present disclosure provides a system and method for controlling ahydraulic pump system. A swashplate type axial piston hydraulic pump mayhave a swashplate tiltable about a swashplate tilt axis, a barrel withaxial pistons disposed in the barrel, the barrel and pistons beingrotatable about a barrel rotation axis relative to the swashplate, thepistons each being moveable relative to the barrel along a straight linepiston path, and the pistons having a stroke determined by the positionof the swashplate. A fluid-powered actuator may be drivingly connectedto the swashplate for displacing the swashplate about the swashplatetilt axis in response to fluid power provided thereto. An electricalcontroller may generate electrical command signals in response tocontroller inputs, and communicate such control signals to a fluid powercontrol device. The fluid power control device is responsive to thecontrol signals to vary fluid power provided to the actuator and thuschange a tilt angle of the swashplate.

In addition, the present disclosure further provides enhanced controlmethods for a utility vehicle, such as a vehicle employing a hydrostatictransmission. More particularly, a speed of an implement, such as ablade, may be maintained at an optimal speed. In this regard, a speed ofa prime mover that powers the implement maybe varied to obtain optimalimplement speed, and/or a mechanical ratio between the prime mover andthe implement may be varied to obtain optimum implement speed. Otherfeatures include four-wheel steering, optimal operating point control(e.g., operating the prime mover at the optimal operating speed andcontrolling speed by varying a ratio of a mechanical coupling betweenthe prime mover and, for example, an implement), cruise control andground speed range control (e.g., altering speed control resolution).

According to one aspect of the invention, a pump control systemincludes: a pump including a swash plate tiltable about a swashplatetilt axis, wherein rotation of the swashplate changes the tilt angle andeffects a change in volumetric displacement of the pump; an actuatordrivingly coupled to the swashplate, the actuator operative to displacethe swashplate about the tilt axis to change the volumetric displacementof the pump; and a fluid power control device operative to vary fluidpower provided to the actuator in response to a control signal; and acontroller operatively coupled to the fluid power control device, thecontroller configured to generate the control signal to modulate thefluid power provided by the fluid power control device to the actuatorto effect rotation of the swashplate.

According to one aspect of the invention, the system includes an inputdevice operatively coupled to the controller, the input device operativeto provide an input command corresponding to an output characteristic ofa hydrostatic transmission, wherein the controller is configured tocontrol an angular orientation of the swashplate based on the inputcommand.

According to one aspect of the invention, the system includes a sensorcommunicatively coupled to the controller, the sensor operative todetect an angular position of the swashplate and to provide the detectedangular position to the controller.

According to one aspect of the invention, the controller is configuredto effect rotation of the swashplate independent of a user suppliedcommand.

According to one aspect of the invention, the fluid power control devicecomprises an electronically-operated valve.

According to one aspect of the invention, the electronically-operatedvalve comprises a pressure control valve.

According to one aspect of the invention, the actuator comprises ahydraulic actuator.

According to one aspect of the invention, the hydraulic actuatorcomprises a linear actuator or a rotary actuator.

According to one aspect of the invention, the actuator is directlycoupled to the swashplate.

According to one aspect of the invention, the actuator is indirectlycoupled to the swashplate.

According to one aspect of the invention, the actuator comprises aball-screw actuator.

According to one aspect of the invention, the system includes aprime-mover coupled to the pump and operative to provide mechanicalpower to the pump module.

According to one aspect of the invention, the system includes ahydrostatic transmission.

According to one aspect of the invention, a zero-turn lawn mowerincludes a prime mover, and a hydrostatic transmission having aswashplate control system as described herein.

According to one aspect of the invention, the system includes a methodfor controlling volumetric displacement of a hydraulic pump having aswash plate tiltable about a swashplate tilt axis is provided, whereinrotation of the swashplate changes the title angle and effects a changein volumetric displacement of the pump. An actuator is drivingly coupledto the swashplate, the actuator operative to displace the swashplateabout the tilt axis to change the volumetric displacement of the pump.The method includes using an electronic controller to modulatinghydraulic power provided to the actuator to effect rotation of theswashplate.

According to one aspect of the invention, modulating hydraulic powerincludes using a fluid power control device to modulate fluid power tothe actuator.

According to one aspect of the invention, the method includes: receivingat the controller a user-initiated command corresponding to an outputcharacteristic of the hydrostatic transmission; and controlling anangular orientation of the swashplate based on the user-initiatedcommand.

According to one aspect of the invention, the method includes: receivingat the controller position data corresponding to an angular orientationof the swashplate; and controlling an angular orientation of theswashplate based on the position data.

According to one aspect of the invention, using the electroniccontroller to modulate hydraulic power provided to the actuator includesmodulating pressure independent of a user supplied command.

According to one aspect of the invention, a vehicle includes: a pumpincluding a swashplate tiltable about a swashplate tilt axis, whereinrotation of the swashplate changes the title angle and effects a changein volumetric displacement of the pump; a controller operatively coupledto the swashplate to effect rotation of the swashplate, the controllerincluding a processor and memory; and logic stored in the memory andexecutable by the processor, the logic configured to automaticallycontrol at least one vehicle characteristic independent of a user inputcommand.

According to one aspect of the invention, the controller is configuredto effect rotation of the swashplate through application of fluid powerto the swashplate.

According to one aspect of the invention, the logic configured toautomatically control at least one vehicle characteristic independent ofa user input command includes logic configured to effect rotation of theswashplate independent of the user input command.

According to one aspect of the invention, the vehicle includes a primemover for providing power to the vehicle, wherein the logic configuredto automatically control at least one vehicle characteristic independentof a user input command includes: logic configured to determine anoptimal operating speed for the prime mover based on at least one systemcondition or ambient condition; and logic configured to regulate theprime mover speed at the optimal operating speed.

According to one aspect of the invention, the vehicle includes: animplement drivingly coupled to the prime mover; a plurality of wheelsdrivingly coupled to the prime mover; and logic configured to alter adrive ratio between the implement and the prime mover so as to maintainthe implement speed at a first prescribed speed, or alter a drive ratiobetween the prime mover and the plurality of wheels so as to maintainthe wheel speed about a second prescribed level.

According to one aspect of the invention, the logic configured toautomatically control at least one vehicle characteristic independent ofa user input command includes logic configured to automatically controla wheel speed of the vehicle independent of the user input command.

According to one aspect of the invention, the vehicle includes: at leastone implement, wherein the controller is operatively coupled to the atleast one implement; and wherein the configured to automatically controlat least one vehicle characteristic independent of the user inputcommand includes logic configured to regulate, independent of the userinput command, a speed of the at least one implement at a prescribedspeed.

According to one aspect of the invention, the at least one implementcomprises mower blades.

According to one aspect of the invention, the vehicle includes a primemover drivingly coupled to the at least one implement, wherein the logicconfigured to regulate a speed of the at least one implement includeslogic configured to vary a speed of the prime mover to regulate theimplement speed at the prescribed speed.

According to one aspect of the invention, the vehicle includes a primemover speed sensor operatively coupled to the prime mover, wherein thelogic configured to vary a speed of the prime mover includes logicconfigured to use data from the prime mover speed sensor to vary thespeed of the prime mover.

According to one aspect of the invention, the vehicle includes a primemover drivingly coupled to the at least one implement, wherein the logicconfigured to regulate a speed of the at least one implement includeslogic configured to vary a drive ratio between the prime mover and theat least one implement to maintain the implement speed at the prescribedspeed.

According to one aspect of the invention, the vehicle includes a speedsensor operatively coupled to the at least one implement, wherein thelogic configured to vary a drive ratio includes logic configured to usedata from the implement speed sensor to control the drive ratio.

According to one aspect of the invention, the vehicle includes logicconfigured to alter resolution of a speed input command based on anoperating mode of the vehicle.

According to one aspect of the invention, the logic configured to alterresolution of a speed input command based on an operating mode of thevehicle include logic configured to increase a maximum speed of thevehicle and decrease a sensitivity of a speed control input when in afirst mode, and decrease a maximum speed of the vehicle and increase thesensitivity of the speed input command when in a second mode.

According to one aspect of the invention, the vehicle includes a firstdriven wheel arranged on a first side of the vehicle; a second drivenwheel arranged on a second side of the vehicle; at least one steerablewheel; at least one steering attitude sensor coupled to the at least onesteerable wheel and to the controller, the attitude sensor operative tocommunicate a steering attitude of the at least one wheel to thecontroller; and at least one steering actuator operatively coupled tothe at least one steerable wheel and to the controller, wherein thelogic configured to automatically control at least one vehiclecharacteristic independent of a user input command includes logicconfigured to command the at least one steering actuator to turn the atleast one steerable wheel based on a speed differential between the atleast two driven wheels and data provided by the steering attitudesensor.

According to one aspect of the invention, the at least one steerablewheel comprises a plurality of steerable wheels, each wheel operativelycoupled to a respective steering actuator and attitude sensor.

According to one aspect of the invention, the vehicle includes ahydrostatic transmission.

According to one aspect of the invention, a vehicle controller isprovided for operating a vehicle including a pump having a swashplatetiltable about a swashplate tilt axis, wherein rotation of theswashplate changes the title angle and effects a change in volumetricdisplacement of the pump. The controller includes: a processor andmemory; and logic stored in the memory and executable by the processor,the logic configured to effect rotation of the swashplate independent ofa user input command.

According to one aspect of the invention, the controller includes logicconfigured to automatically control at least one vehicle characteristicindependent of a user input command.

According to one aspect of the invention, the controller includes: logicconfigured to determine an optimal operating speed for a prime moverbased on at least one system condition or ambient condition; and logicconfigured to regulate a prime mover speed at the optimal operatingspeed.

According to one aspect of the invention, the logic configured toautomatically control at least one vehicle characteristic independent ofa user input command includes logic configured to automatically controla wheel speed of the vehicle independent of the user input command.

According to one aspect of the invention, the controller includes logicconfigured to regulate, independent of a user input command, a speed ofat least one implement at a prescribed speed.

According to one aspect of the invention, the controller includes logicconfigured to alter resolution of a speed input command based on anoperating mode of the vehicle.

According to one aspect of the invention, the logic configured toautomatically control at least one vehicle characteristic independent ofa user input command includes logic configured to command at least onesteering actuator to turn at least one steerable wheel based on a speeddifferential between at least two driven wheels and data provided by asteering attitude sensor.

The foregoing and other features of the invention are hereinafterdescribed in greater detail with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an exemplary zero-turn-radius moweremploying a hydrostatic transmission to which the principles of theinvention can be applied, as discussed below.

FIG. 2 is a block diagram of an exemplary control system in accordancewith aspects of the present invention.

FIG. 3 is a schematic diagram of an exemplary control system inaccordance with an embodiment of the present invention.

FIG. 4 is a schematic diagram illustrating a fluid-powered rotaryactuator that may be used in a control system in accordance with thepresent invention.

FIG. 5 is a schematic diagram of another exemplary control system inaccordance an embodiment of the present invention.

FIG. 6 is a block diagram illustrating an exemplary regulator that canbe used to control swashplate position in accordance with the presentinvention.

FIG. 7 is a perspective view of certain components of an exemplary pumpthat may be used in accordance with the present invention.

FIG. 8 is an enlarged perspective view of certain other components of anexemplary pump that may be used in accordance with the presentinvention.

FIG. 9 is a block diagram illustrating exemplary architecture that canbe used to implement tip speed control in accordance with one aspect ofthe disclosure.

FIG. 10 is a flow chart illustrating exemplary steps for performing tipspeed control using the architecture of FIG. 9.

FIG. 11 is a block diagram illustrating exemplary architecture that canbe used to implement tip speed control in accordance with another aspectof the disclosure.

FIG. 12 is a flow chart illustrating exemplary steps for performing tipspeed control using the architecture of FIG. 11.

FIG. 13 is a block diagram illustrating exemplary architecture forimplementing cruise control in accordance with one aspect of thedisclosure.

FIG. 14 is a flow chart illustrating exemplary steps for performingcruise control using the architecture of FIG. 13.

FIG. 15 is a flow chart illustrating exemplary steps for performingground speed range control using the architecture of FIG. 13

FIG. 16 is a flow chart illustrating exemplary steps for performingoptimal operating point control using the architecture of FIG. 13.

FIG. 17 is a block diagram illustrating exemplary architecture forimplementing four-wheel steering in accordance with one aspect of thedisclosure.

FIG. 18 is a block diagram illustrating exemplary architecture forimplementing four-wheel steering in accordance with another aspect ofthe disclosure.

FIG. 19 is a flow chart illustrating exemplary steps for performingfour-wheel steering using the architecture of FIG. 17 or 18.

DETAILED DESCRIPTION

Aspects of the present invention will now be described in the context ofa hydrostatic transmission of a zero-turn-radius mower. It should beappreciated, however, that aspects of the invention are applicable toother applications in which a hydrostatic transmission is utilized.

Referring now to the drawings in detail, and initially to FIG. 1, anexemplary zero-turn-radius mower 10 is illustrated. It is noted that thedesign of the illustrated mower 10 is merely exemplary in nature, and itwill be appreciated that other mower designs and vehicle types can beused in accordance with the invention.

The mower 10 includes a frame 12, a mower deck 14 supported by the frame12 for mowing grass, an operator seat 16, and a plurality of controls 18for operating the mower 10. A rear mounted engine attached to the frame12 behind the seat 16 provides power to left and right hydrostatictransmissions also mounted to the frame 12 (the engine and hydrostatictransmissions are not shown in FIG. 1). As will be described in moredetail below, each hydrostatic transmission includes a hydraulic pumphaving a swashplate, the swashplate operative to vary a volumetricdisplacement of the respective hydraulic pump.

A controller 20 is attached to the frame 12 and preferably located in anenclosure or other protected area. In the embodiment shown in FIG. 1 thecontroller 20 is located under the seat 16, although other locations arecontemplated. As will be described in more detail below, the controller20 is operatively coupled to the plurality of controls 18 and to theswashplate of each hydrostatic transmission. Based on commands receivedfrom the controls 18, the controller 20 can control the hydrostatictransmissions to independently drive respective rear wheels 22 to propelthe mower and provide zero-turn-radius functionality.

With reference to FIG. 2, a block diagram is provided illustrating thegeneral architecture of a control system 30 in accordance with thepresent invention. More specifically, the system 30 includes theaforementioned controller 20, which can include a processor forexecuting instructions and a storage device, such as memory, for storinginstructions executable by the processor. Alternatively, the controller20 may be in the form of a dedicated circuit, such as anapplication-specific integrated circuit (ASIC) or other custom circuit.

The controller 20 is operatively coupled to a user interface module 32(also referred to as an input device) to receive inputs for operatingthe mower 10. Generally, the user interface module 32 converts operatorcommands into signals that can be read by the controller 20. Thus, forexample, the user interface module 32 can include the plurality ofoperator controls 18 and sensing devices operatively coupled thereto,the sensing devices operative to convert, for example, linear or rotarymotion into signals readable by the controller 20 (e.g., analog voltageor current signals, digital signals, etc.). The signals provided to thecontroller 20 may correspond to a desired output characteristic of thehydrostatic transmission (e.g., speed, power, torque, swashplateposition, etc.).

Exemplary operator controls include a steering wheel, pedals, lap bars,joysticks and the like, while exemplary sensors include potentiometers,encoders, resolvers, and the like. The operator controls 18 may alsoinclude devices that provide binary on/off data, e.g., selectorswitches, pushbuttons and the like. Based on data received by thecontroller 20 from the user interface module 32, the controller 20generates a control signal for regulating a position of a swashplate ofthe hydrostatic transmission.

A power module 34 provides fluid or electric power to the system. Insome embodiments the power module 34 may be fluid power provided by apump (e.g., pneumatic or hydraulic power). In other embodiments thepower module 34 may provide electric power. Power provided by the powermodule 34 is provided to a regulator module 36.

The regulator module 36 receives the power provided from the powermodule 34 and the control signal from the controller 20. Based on thecontrol signal from the controller 20, the regulator module 36 modulatesthe power (e.g., pressure or voltage) at its output and provides themodulated power to an actuator module 38. The actuator module 38includes an actuator, such as a pneumatic, hydraulic or electricactuator, which may be in the form of a linear or rotary actuator.Modulation of the power provided to the actuator module 38 produces adesired displacement of the actuator.

A pump module 40 includes a hydraulic pump having a rotatable swashplateto vary displacement of the pump, the swashplate being operativelycoupled to the actuator of the actuator module 26. By virtue of thecoupling between the actuator and the swashplate, displacement of theactuator also effects angular displacement of the swashplate.

Accordingly, pump displacement (and thus power output by eachhydrostatic transmission) is electronically controlled by the controller20. Such control by the controller 20 is advantageous in that it enablesrotation of the swashplate independent of a user-supplied command.Independent control can be useful for implementing custom control modesfor the mower 10, such as cruise control, optimal implement speedcontrol, four-wheel steering control, etc.

With additional reference to FIG. 3, a schematic representation of acontrol system 50 in accordance with FIG. 2 is shown for a system usinghydraulically actuated swashplate. While a hydraulic system isillustrated in FIG. 3, it should be appreciated that other types offluid power may be utilized without departing from the scope of theinvention. For example, instead of hydraulic power the system mayutilize pneumatic power.

As shown in FIG. 3 a hydrostatic transmission 52 includes a variabledisplacement hydraulic pump 54 for generating hydraulic power used bythe hydrostatic transmission 52. The hydraulic pump 54 may be driven bya prime mover 56, such as an internal combustion engine, an electricmotor or the like via drive system 58 (e.g., belt drive, chain drive,gear drive, etc.). Hydraulic power generated by the pump 54 is providedto a hydraulic motor 60 of the hydrostatic transmission 52 via ports,conduits and/or lines (not shown) within the hydrostatic transmission52. The hydraulic motor 60 converts the hydraulic power received fromthe pump 54 into rotational power, which is provided at the output shaft62 for driving wheels 22.

The hydraulic pump 54 includes a rotatable swashplate 64, wherevariation of the angular position of the swashplate 64 varies its tiltangle and thus displacement of the pump 54 (e.g., between a minimumdisplacement (e.g., approximately 0%) and a maximum displacement (e.g.,100%)). An angle sensor 66 monitors the swashplate 64 to detect anangular position of the swashplate 64. The sensor 66 may be in the formof an encoder, a resolver, a hall effect sensor or other suitable sensorfor detecting angular position or displacement. The sensor may directlymonitor position of the swashplate 66, or indirectly monitor theposition of the swashplate (e.g., via a trunnion shaft).

Operatively coupled to the swashplate 64 are first and second hydrauliccylinders 68 and 70. The cylinders 68 and 70 may be indirectly coupledto the swashplate 64. For example, the swashplate 64 may include atrunnion shaft 73 that effects rotation of the swashplate, the trunnionshaft being coupled to the cylinders 68 and 70 via arms 68 a and 70 a.Alternatively, the cylinders 68 and 70 may be directly coupled to theswashplate 64. Linear displacement of the first cylinder 68 effectsrotation of the swashplate 64 in a first direction, and lineardisplacement of the second cylinder 70 effects rotation of theswashplate 64 in a second direction opposite from the first direction.

The first and second cylinders 68 and 70 are in fluid communication withfirst and second fluid power control devices 72 and 74, respectively.First and second fluid power control devices 72 and 74, which in thepresent example are two-way valves, receive hydraulic power from ahydraulic power source 76, such as a fixed-displacement pump driven bythe prime mover 56. While the exemplary embodiment utilizes two-wayvalves, other devices may be used, e.g., three-way valves.

Although linear actuators are described in the present embodiment, othertypes of actuators may be used without departing from the scope of theinvention. For example, instead of linear actuators, rotary actuatorsmay be utilized. Briefly, FIG. 4 illustrates use of rotary actuators ina hydraulic system. The system is similar to the hydraulic portion ofFIG. 3, except the first and second actuators 68 and 70 are replacedwith a rotary hydraulic actuator 67. In response to hydraulic powerprovided by the fluid power control devices 72 and 74 to the rotaryactuator 67, rotation of an output shaft 67 a in a forward or reversedirection is achieved. The output shaft 67 a may be directly coupled tothe trunnion shaft 73 of the swashplate 64, or optionally a gearbox 67 bmay be arranged between the output shaft 67 a and the trunnion shaft 73.

Additionally, while not shown in FIG. 3 or 4 the system can include anadjustment device to set a neutral position for the hydraulic actuators.The adjustment device is manipulated during a calibration procedure toreturn the cylinders 68 and 70 (or rotary actuator 67) to a neutralposition and remain in that position during power loss.

The controller 20 includes one or more outputs for providing controlsignals, status signals, etc. to other devices, such as the fluid powercontrol devices 72 and 74. For example, first and second outputs 78 and80 of the controller are operatively coupled to the first and secondfluid power control devices 72 and 74, respectively, to provide firstand second control signals (e.g., analog signals such as 0-10 VDC or4-20 mA signals) to the respective fluid power control devices 72 and74. The first and second control signals are proportional to a desiredfluid flow through the fluid power control devices, or proportional to adesired fluid pressure at the output of the fluid power control devices.In this regard, 0 VDC (or 4 mA) may correspond to no fluid flow or nopressure, while 10 VDC (or 20 mA) may correspond to 100% fluid flow or100% pressure. In this manner, the controller 20 can control thedelivery of fluid power to the actuators 68 and 70. While analog signalsare described in the present example, other signal types may be utilizedwithout departing from the scope of the invention. For example, insteadof using outputs embodied as analog outputs, control signals may becommunicated to the valves 72 and 74 (or other devices) via acommunication bus (e.g., a network). The controller may includeadditional outputs that may be used by the system, such as wheel speedreference signals, implement speed reference signals, or any otherparameter that may be controlled by the controller 20. Such outputs maybe used to provide enhanced control functions.

The controller 20 includes one or more inputs for receiving data fromother devices, such as the operator controls 18. For example, thecontroller 20 includes a first input 82 for receiving an input commandfrom a user-operated device, such as a speed command, a power command, adirection command, etc. For sake of clarity only one input is shown forthe operator controls. It will be appreciated, however, that thecontroller 20 may have a plurality of inputs as needed for therespective operator controls. As discussed above, the user operateddevice may be coupled to a sensor 86 so as to convert linear or rotarymotion into a signal readable by the controller 20. The controller 20also includes a second input 84 communicatively coupled to the anglesensor 66 for receiving data corresponding to an angular position of theswashplate 64. The controller 20 may optionally include other inputs fordetecting various parameters, such as, for example, power take offengaged/disengaged, prime mover speed, implement speed, wheel speed, orany other parameter that may be used by the controller 20. The inputsmay be analog inputs (e.g., 0-10 VDC, 4-20 mA, etc.), digital inputs,optical inputs, networks, or other conventional means for providing datato the controller 20.

Referring to FIG. 5, another embodiment of a control system 50′ inaccordance with the present invention is illustrated. The system 50′ issimilar to the system 50 of FIG. 3, except that electrically-operatedactuators are used instead of hydraulically operated actuators. Moreparticularly, the hydrostatic transmission 52 and its subcomponents(hydraulic pump 54 and swashplate 64, hydraulic motor 60), the primemover 56, drive system 58, angle sensor 66, controller 20 and associatedI/O are the same as those in the system of FIG. 3. Therefore, discussionof these components will be omitted for FIG. 5.

The system 50′ includes first and second electrically-operated actuators69 and 71 operatively coupled to the swashplate 64. Stepper motors,servo motors, shape memory alloys and piezoelectric actuators areexamples of electrically-operated actuators that may be used inaccordance with the present invention. The electrically-operatedactuators 69 and 71 may be indirectly coupled to the swashplate 64. Forexample, the swashplate 64 may include a trunnion shaft 73 that effectsrotation of the swashplate 64, the trunnion shaft being coupled to theelectrically-operated actuators 69 and 71 via arms 68 a and 70 a.Alternatively, the electrically-operated actuators 69 and 71 may bedirectly coupled to the swashplate 64. Linear displacement of the firstelectrically-operated actuator 69 effects rotation of the swashplate 64in a first direction, and linear displacement of the secondelectrically-operated actuator 71 effects rotation of the swashplate 64in a second direction opposite from the first direction.

While linear electrically-operated actuators are described in thepresent embodiment, other types of electrically-operated actuators maybe used without departing from the scope of the invention. For example,a bi-directional linear actuator or a rotary actuator may be utilized.In one embodiment, the linear actuator is a motor-driven ball-screwarrangement.

The electrically-operated actuators 69 and 71 receive power from anelectrical power source 77. The electrical power source 77, for example,may be an alternator or generator driven by the prime mover 56.Alternatively, the electrical power source 77 may be a battery.

The electrically-operated actuators 69 and 71 are operatively coupled tothe controller 20 via outputs 78 and 80. The outputs may be analogoutputs that provide a voltage or current control signal as describedwith respect to the embodiment of FIG. 3, a communication network thatprovides digital control signals to the actuators, or any other meansfor communicating the control signals to the actuators 69 and 71. Basedon the control signals, the electrically operated actuators 69 and 71rotate the swashplate 64 into any one of a number of differentpositions.

Regardless of the form of the actuators (i.e., hydraulic or electric),the controller 20 includes logic configured to position the swashplate64 so as to produce a desired characteristic from the hydrostatictransmission 52 (e.g., output power, output speed, output torque, etc.).The logic may be stored in memory of the controller 20 and executable bya processor of the controller 20. The logic stored in the controller 20may be configured to control the position of the swashplate 64independent of a user input command, or based on a user-command providedby the plurality of controls 18. For example, a specific function of thevehicle, such as cruise control, can be executed by the controller 20 toregulate the position of the swashplate to achieve a desired speed,without input from the user. Alternatively or additionally, theplurality of user-operated controls 18, such as a foot-operated pedal, ahand-operated lever, or the like can be operatively coupled to arespective sensor 86 to provide a signal corresponding to displacementof the pedal or lever (or other device). The signal generated by thesensor 86 can be provided to the controller 20 via the first input 82.The controller 20 can equate a low end of the signal range (e.g., 0 VDC,4 mA) to a first angular position of the swashplate 64 corresponding tominimum pump displacement, and a high end of the signal range (e.g., 10VDC, 20 mA) to a second angular position of the swashplate 64corresponding to a maximum pump displacement. The user-input signal maybe filtered and scaled as is conventional.

The logic executed by the controller 20 may include a position regulatorfor controlling a position of the swashplate 64. In this regard, thesignal generated from the sensor 86 can be a “reference” position forthe swashplate 64, and the signal provided by the angle sensor 66 can bethe “actual” position of the swashplate 64. Based on a differencebetween the reference position and the actual position, the positionregulator may generate a control signal, which may be filtered andscaled as is conventional. The control signal may be provided to one ofthe fluid power control device 72 and 74 (or to theelectrically-operated actuators 69 and 71) via the outputs 78 and 80 ofthe controller 20. In response to the control signal, the fluid powercontrol devices 72 or 74 will alter the fluid flow and/or fluid pressureprovided to the actuators 68 or 70, thereby causing actuatordisplacement and effecting rotation of the swashplate 64. Alternatively,in response to the control signal the electrically-operated actuators 69and 71 will utilize the electrical power from the power source 77 toproduce actuator displacement, thus effecting rotation of the swashplate64.

With reference to FIG. 6, an exemplary position regulator 100 isillustrated in block form, the position regulator 100 being executableby the controller 20 to control an angular orientation of the swashplate64. Beginning at block 102, the controller 20 receives the user inputsignal for controlling a feature of the hydrostatic transmission, e.g.,output velocity. The user input signal may be a signal obtained from theuser interface module 32. For example, and as described herein, the usermay manipulate an operator control 18, which in turn causes a sensor 86coupled to the operator control 18 to generate a signal. The signal,which may be an analog signal, a digital signal, an optical signal orany other signal readable by the controller 20, preferably isproportional displacement of the respective operator control. Thegenerated signal is read by the controller 20 via an input modulecorresponding to the type of signal (e.g., an analog voltage signalwould be input via an analog voltage input). Next at block 104 the userinput signal is optionally scaled and filtered to produce a signalcorresponding to the regulated parameter. In the example shown in FIG.6, the user input signal may be scaled to correspond to the feedbackdevice coupled to the swashplate (i.e., sensor 66). In this regard, theuser input signal could be scaled to correspond to swashplate angularorientation. Based on such scaling, the output of block 104 is aposition reference signal and is provided to a positive input of summingjunction 106.

As described herein, an angular position of the swashplate 64 isdetected by sensor 66 and is provided to the controller 20 at block 108.The sensor signal may be analog, digital, optical or any other signaltype readable by the controller 20. Next at block 110, the positionfeedback signal is optionally scaled and filtered to correspond to theposition reference signal, and the position feedback signal then isprovided to a negative input of summing junction 106. The output of thesumming junction is an error signal indicative of the error between thedesired position of the swashplate 64 and the actual position of theswashplate 64. The error signal is provided to an input of controller112, which is shown as a proportional-plus-integral-plus-derivative(PID) controller, although other controllers may be used (e.g., aproportional controller, a proportional-plus-integral controller, etc.).

Based on the error signal the controller 112 generates a control signal,which is output by the controller at block 114 and provided to theactuator (e.g., to one of the fluid power control devices 68 or 70 inFIG. 3 or to one of the electrical actuators 69 and 71 in FIG. 5). Inresponse to the control signal, displacement of the actuator and thus ofthe swashplate 64 is effected.

While the exemplary embodiment is described in the context of a positionregulator, it should be appreciated that other regulation schemes may beemployed without departing from the scope of the invention. For example,a speed regulator, torque regulator, power regulator, etc. may be usedinstead of or in conjunction with the position regulator.

Referring now to FIGS. 7-8, each hydrostatic transmission 52 includes aconventional over center swashplate type axial piston hydraulic pump 54.Pump 54 includes an input 120 that is drivingly connected to prime mover56 to rotate a pump barrel 122. A plurality of axial pistons 124 aredisposed within the pump barrel 122 and rotate with the pump barrel 122about a barrel axis 126. Pump 54 also includes a conventional overcenter swashplate 64 which is tiltable about a swashplate tilt axis 128.The pistons 124 are each moveable relative to the barrel along astraight line piston path 130 that is substantially parallel to thebarrel rotation axis 126, and the pistons 124 have a stroke determinedby the position of the swashplate 64. When the swashplate 64 is in aneutral or center position perpendicular to the barrel axis 126, thestroke of the pistons 124 is substantially zero and the output fluidflow displacement from the pump 54 is substantially zero. When theswashplate 64 begins to be displaced or titled in either direction aboutits tilt axis 128, the stroke of pistons 124 begins to increase andoutput fluid flow displacement from the pump 54 begins. As the tiltangle of the swashplate 64 increases, the stroke of pistons 124increases and the output fluid flow displacement from the pump 54increases in a known manner. The output fluid flow displacement frompump 54 will be in one direction when the swashplate 64 is tilted in onedirection from its neutral position and will be in the other directionwhen the swashplate 64 is tilted in the opposite direction. The outputfluid flow from each pump 54 of each hydrostatic transmission flowsthrough conduits (not shown) to a hydraulic motor 60 (FIG. 3) of eachhydrostatic transmission 52, and such output flow rotates its associatedhydraulic motor 60 to rotate its associated wheel 22 in the forward orreverse direction in a known manner. A reservoir 132 provides hydraulicfluid to the pump 54, and a lever 134 opens and closes a fluid by-passroute (not shown) to enable pushing vehicle 10 when required.

Referring now to FIG. 9, there is provided a block diagram illustratingexemplary architecture 200 for a vehicle, such as a zero-turn mower orother utility vehicle, equipped with implement speed control inaccordance with the present disclosure. The exemplary vehicle mayinclude a hydrostatic transmission incorporating the pump systemdescribed herein.

The vehicle includes a prime mover 56, such as an internal combustionengine, electric motor, or the like for providing power to the vehicleand subsystems. A speed sensor 202, such as a tachometer, encoder,resolver or other speed sensing device, is coupled to the prime mover 56so as to detect a speed of the prime mover 56. The speed sensor 202,which is also communicatively coupled to the controller 20, converts thesensed speed into a form readable by the controller 20 (e.g., an analog,digital or optical signal). In this manner, the controller 20 canmonitor the speed of the prime mover 56.

Further, the prime mover 56, via an output shaft, provides power to apower take-off unit 204, such as an electromagnetic clutch coupled to agear drive, belt drive, or other means for transferring power from theprime mover 56 to another device. The power take-off unit 204 mayinclude a power input shaft (not shown) coupled to the prime mover 56,and a power output shaft (not shown) coupled to subsystems of thevehicle. When the power take-off unit 204 is in a disabled state nopower is transferred from the power input shaft to the power outputshaft, and when the power take-off unit 204 is in an enabled state poweris transferred from the power input shaft to the power output shaft.

A power take-off controller 206 is coupled to the power take-off unit204, the power take-off controller 206 operative to selectivelyenable/disable the power take-off unit 204, thereby selectively couplingthe power input shaft to the power output shaft. In one embodiment, thepower take-off controller 206 is an electric switch and the powertake-off unit 204 is an electromagnetic clutch coupled to a belt-drivenpulley system.

The power take-off controller 206 includes a sensor (not shown) fordetecting the status (i.e., enabled or disabled) of the power take-offunit 204. In one embodiment, the sensor is in the form of a switch, suchas a mechanical or optical switch, where switch contacts are closed whenthe power take-off unit 204 is in the enabled state. Data from thesensor (e.g., contact closure) is provided to the controller 20 forcontrolling the system, as described in more detail below.

Also coupled to the power take-off unit 204 is an implement 208, such asa mower deck that includes one or more rotating blades. Other types ofimplements include, for example, a flail mower, rotary cutter, rotarybroom, blower and snow thrower. In the configuration of FIG. 9,implement speed is directly related to the prime mover speed.

A prime mover speed controller 210 is coupled to the prime mover 56 andoperative to control prime mover speed. In one embodiment, the primemover 56 is an internal combustion engine and the prime mover speedcontroller 210 is a throttle plate controller of the internal combustionengine. The controller 20, based on the sensed speed as provided by theprime mover speed sensor 202, commands the prime mover speed controller210 to open or close the throttle plate, thereby changing the primemover speed. Accordingly, the controller 20 can control implement speedby controlling prime mover speed.

For utility vehicles/tractors such as zero turn mowers, regulatory andstandard compliance issues may govern the maximum operating speed ofvehicle mounted implements. For example, the tip speed of mower bladesis limited to 19,000 feet per minute by ANSI B71.4. The state of the artfor driving implements is a constant ratio between implement and primemover. For example, a mower deck is designed not to exceed the maximumallowable tip speed in the worst case tolerance stack up and the highend of the engine speed high idle setting. In practice, however, theengine speed will drop 5-10% simply due to engagement of the deck, andwill drop even further during operation. Typically, the gap between highidle engine speed and the peak power engine speed approaches 20%. Theresult is that the tip speed during operation is 10-20% less than themaximum allowable.

For many implements, limiting implement speed limits the operatingcapability of the implement. In addition, end users may place value onhaving the highest possible operating speed available in theirequipment. For example, in the mowing market many people generallybelieve that “tip speed=quality of cut”.

Referring now to FIG. 10, illustrated is a flow chart 250 that includesexemplary steps for controlling implement speed in the system of FIG. 9.The steps shown in FIG. 10 may be executed by the controller 20.

Beginning at block 252, the status of the power take-off unit 204 isdetermined, for example, using the sensor within the power take-offcontroller 206. If it is determined the power take-off unit 204 isdisabled, the process loops at block 252. However, if the power take-offunit 204 is enabled, then at block 254 the actual speed of the primemover 56 is determined. The speed may be determined, for example, fromdata provided by the prime mover speed sensor 202.

Next at block 256 the actual speed of the prime mover is compared to atarget speed. The prime mover target speed may be a predetermined speedbased on a known mechanical ratio between the prime mover output shaftand the power take-off unit output shaft. For example, from the knownmechanical ratio it can be determined that in order to maintain animplement speed of 19,000 feet per minute the prime mover must operateat 4000 revolutions per minute. If at block 256 the prime mover actualspeed is at the prime mover target speed, then at block 258 the primemover speed controller 210 is commanded to maintain the prime moverspeed, and then the method moves back to block 252 and repeats.Alternatively, if at block 256 the prime mover actual speed is not equalto the prime mover target speed, then at block 260 the prime mover speedcontroller 210 is commanded to increase or decrease the prime moverspeed to obtain the target speed, and then the method moves back toblock 252 and repeats. Alternatively, the system may be configured toreduce prime mover speed only when the implement speed is above aspecified limit.

Accordingly, in the embodiments shown in FIGS. 9 and 10 implement speedis maintained at the optimal speed by controlling the speed of the primemover 56.

Moving now to FIG. 11, a block diagram is provided that illustratesanother exemplary architecture 220 for tip speed control for use with avehicle in accordance with the present disclosure. Like the embodimentshown in FIG. 9, the architecture of FIG. 11 includes a prime mover 56,power take-off unit 204, power take-off controller 206, implement 208and controller 20. The prime mover 56, power take-off unit 204, powertake-off controller 206 and implement 208 may be the same as thosedescribed in FIG. 9 and therefore these components will not be describedagain here. The prime mover 56, however, does not require an associatedprime mover speed controller or a prime mover speed sensor. Instead, theprime mover 56 is commanded to operate at a fixed speed, for example,based on a throttle position as set by a user. In such configuration, itis possible that the prime mover speed will not be optimal or may driftbased on external influences, e.g., enabling or disabling the implement,the throttle setting being less than maximum, ambient conditions, etc.As a result, the implement speed may not be at the optimal speed and/ormay drift from the optimal speed.

In accordance with the embodiment of FIG. 11, an implement speed sensor212 is coupled to the implement and is operative to detect a speed ofthe implement. The implement speed sensor 212 converts the detectedimplement speed into a form readable by the controller 20 (e.g., analog,digital, optical, etc.). The implement speed sensor 214 may be atachometer, encoder, resolver or other speed sensing device. Inaddition, an implement speed controller 214 is operatively coupled tothe implement 208, the implement speed controller 214 configured to varya drive ratio between the implement 208 and the power take-off unit 204.In one embodiment, the implement speed controller 214 comprises acontinuously variable transmission. By altering a drive ratio betweenthe implement 208 and the power take-off unit 206, implement speed canbe maintained at an optimal level or below an allowable level, even whenprime mover speed droops or varies. This allows the implement to runnear optimal speed during normal operation, rather than to operate atallowable implement speed when engine speed is a maximum (a conditionthat rarely, if ever, occurs).

With reference to FIG. 12, illustrated is a flow chart 270 that includesexemplary steps for controlling implement speed using the architectureshown in FIG. 11. The steps shown in FIG. 12 may be executed by thecontroller 20.

Beginning at block 272, the status of the power take-off unit 204 isdetermined, for example, using the sensor within the power take-offcontroller 206. If it is determined the power take-off unit 204 isdisabled, the method loops at block 272. However, if the power take-offunit 204 is enabled, then at block 274 the actual speed of the implement208 is determined. The speed may be determined, for example, from dataprovided by the implement speed sensor 212.

Next at block 276 the actual speed of the implement 208 is compared to atarget speed. The implement target speed may be a predetermined speedbased on a maximum allowable speed, or may be based on operator input.If at block 276 the implement actual speed is at the target speed, thenat block 278 the implement speed controller 214 is commanded to maintainthe ratio between the implement 208 and the prime mover 56, and themethod moves back to block 272 and repeats. However, if at block 276 theimplement actual speed is not at the target speed, then at block 280 theimplement speed controller 214 is commanded to increase or decrease themechanical ratio between the implement 204 and the prime mover 56 so asto achieve the target implement speed, and then the method moves back toblock 272 and repeats.

Accordingly, in the embodiments shown in FIGS. 11 and 12 implement speedis maintained at the optimal speed or below allowable speed bycontrolling a drive ratio between the implement 208 and the prime mover56.

Moving now to FIG. 13, a block diagram is provided that illustratesanother exemplary architecture 300 for a vehicle in accordance with thepresent disclosure. Like the previous embodiments, the architecture ofFIG. 13 includes a prime mover 56, power take-off unit 204, powertake-off controller 206, implement 208 and controller 20. The primemover 56, power take-off 204, power take-off controller 206 andimplement 208 may be the same as those described in FIG. 9 and thereforethese components will not be described again here.

The prime mover 56 is coupled to left and right trans missions, such ashydrostatic transmissions 52 l and 52 l coupled to a left and rightwheels, respectively (not shown). More specifically, an output shaft ofthe prime mover 56 may be coupled to an input shaft of left and rightfluid pumps as described herein. The left transmission 52 l controls thedelivery of power to the left wheel while the right transmission 52 rcontrols delivery of power to the right wheel. The prime mover also mayoptionally have a speed sensor 202 for detecting a speed of the primemover 56 and communicating the detected speed to the controller 20.

The controller 20 is operatively coupled to the left and right pumps soas to control power output by the hydrostatic transmissions 52 l and 52r. For example, and as described herein, the controller 20 isoperatively coupled to a fluid power control device 72 l or 74 l toselectively control the delivery of fluid power to a left swashplate 64l of the left fluid pump 54 l. A similar configuration is provided forthe right fluid pump 54 r. In this manner, the controller 20 can controlpower output by the left and right transmissions 52 l and 52 rindependent of user input. Additionally, the position of the left andright swashplates 64 l and 64 r may optionally be communicated to thecontroller via left and right angle sensors 66 l and 66 r as describedherein. Based on the detected swashplate position, the controller 20 canadjust the fluid power provided to the respective swashplate. Thecontroller 20 may optionally receive implement speed data from implementspeed sensor 212, and optionally provide commands to implementcontroller 214 as described in embodiment of FIG. 11.

Operator controls 18, such as speed controls, steering controls, etc.,can be provided to the controller 20. The controller 20, for example,based on operator input via the operator controls can command theswashplates 64 l and 64 r to provide a desired power output from thehydrostatic transmissions 52 l and 52 r, as described in more detailwith respect to FIGS. 14 and 15.

Referring to FIG. 14, a flow chart 320 illustrating exemplary steps forimplementing cruise control using a pump control system is provided. Aswill be appreciated, cruise control enables a user to select a speed ofthe vehicle and once engaged, the vehicle will remain at the set speed.

Beginning at block 312, the system determines if cruise control isenabled. Cruise control can be enabled or disabled, for example, via aselector switch, pushbutton, operator interface, etc. accessible by anoperator of the vehicle. Such input may form part of the operatorcontrols 18. If cruise control is not enabled, then at block 314 anyspeed setpoint that may be stored in memory is cleared, and at block 316speed control of the vehicle is under control of the user (e.g., via theoperator speed controls). The method then moves back to block 312 andrepeats.

If at block 312 cruise control is enabled, then at block 318 it isdetermined if cruise control is engaged. Like enabling/disabling cruisecontrol, the feature also can be engaged/disengaged via operator input(e.g., a set or resume pushbutton or other input means). Further, cruisecontrol may be disengaged by certain operator actions, such as pressingon a brake pedal or placing the vehicle in neutral. If cruise control isdisengaged, then at block 320 the speed set point when cruise controlwas last engaged is stored in memory, and the method moves to block 316as described above. However, if at block 318 cruise control is engaged,then at block 322 it is determined if the vehicle is performing a turnoperation. Determining whether or not the vehicle is turning can bebased, for example, on user input (e.g., steering controls), wheelsspeed feedback, swashplate position, etc. If at block 322 it isdetermined the vehicle is turning, then the method moves to block 320and 316 as described above (i.e., speed control is via user input).However, if is determined the vehicle is not turning, then at block 324a speed setpoint is obtained. The speed setpoint may be obtained in anyone of a number of ways. For example, the user may obtain a desiredspeed of the vehicle using the operator speed controls, and then push abutton indicating the current speed is the cruise control speedsetpoint. Such button, for example, may be a conventional button (e.g.,a push button) or a soft button (e.g., a button on a touch screen).

Once the speed setpoint has been set, then at block 326 the actual speedof the vehicle is determined. Such actual speed may be determined fromspeed sensors on the wheels, or inferred from operator controls and/orswashplate position. Having obtained the speed setpoint and the actualvehicle speed, a speed error is calculated based on the differencebetween the speed setpoint and the actual speed, as indicated at block328. At block 330, the speed error is analyzed to determine if thevehicle speed is correct, needs to be increased, or needs to bedecreased. If the actual speed matches the speed setpoint (or is withina predetermined range of the setpoint), then no correction is necessaryand the current speed is maintained as indicated at block 332. If atblock 330 the actual speed is less than the speed set point, then atblock 334 a command is issued to increase the speed. Moving back toblock 330, if the actual speed is greater than the speed set point, thenat block 336 a command is issued to decrease the speed. The speedcommands may be made to the prime mover 56 (e.g., via a prime moverspeed controller as shown in FIG. 9), or the swashplate for each pump(e.g., via fluid control devices 72 and 74 as shown in FIG. 13).

Accordingly, the controller 20 can control a characteristic of thevehicle, such as speed, independent of user commands. In this regard,the controller 20 can vary a swashplate position through the applicationof hydraulic power to the swashplate.

Moving now to FIG. 15, a flowchart 400 is illustrated for implementingground speed range control using the architecture of FIG. 13. Groundspeed range control allows the operator to select various ranges ofground speed operation, trading maximum ground speed for ground speedcontrol resolution as appropriate for the current operation andconditions. For example, when driving for a significant distance maximumground speed is desirable to minimize travel time. For trimming aroundmulch beds, however, fine speed resolution is desired to enhancecontrollability, allowing trimming without scattering mulch, yet closeenough to eliminate the need for secondary hand trimming. Ground speedrange control allows the operator to select (and change upon command)the maximum ground speed, which is then scaled across the full range ofcontrol travel, increasing/decreasing ground speed resolution. Forvehicles that use drive wheel speed differential to accomplish steering(e.g., zero turn mowers), steering resolution also can be enhanced.

Beginning at block 402 it is determined if normal control or modifiedcontrol is enabled. Such determination can be based, for example, onoperator input provided to the controller, e.g., a switch, togglepushbutton, operator interface entry, etc. If normal operation isselected, then at block 404 system control is unchanged and the methodmoves back to block 402. If enhanced resolution is selected, then atblock 406 it is determined if high speed/low resolution or lowspeed/high resolution is desired. Such determination again can be madebased on operator input. For example, a selector switch may have a highspeed setting and a low speed setting. The controller 20 may receivedata from the selector switch and determine the desired setting.Alternatively, the desired range control may be based on an enteredmaximum speed, which may be entered via an operator interface orselector switch.

At block 408 the desired speed resolution is determined. If highresolution control is desired (e.g., low maximum speed), then at block410 maximum deflection of the operator speed control input is associatedwith a low speed, and all lower speed requests are scaled accordingly.For example, if the maximum speed is selected to be 5 MPH, then at fulldeflection of the operator speed input the vehicle speed will be 5 mph,and at 50% deflection of the operator speed input the vehicle speed willbe 2.5 mph. If, on the other hand, low resolution (high speed) isdesired, then at block 412 maximum deflection of the operator speedcontrol input is scaled to the desired high speed, and all lower speedrequests are scaled accordingly. For example, if the maximum speed isselected to be 12 MPH, then at full deflection of the operator speedinput the vehicle speed will be 12 MPH, and at 50% deflection of theoperator speed input the vehicle speed will be 6 MPH. Once the speedrange has been scaled, the method moves back to block 402.

Another feature that may be implemented in accordance with the presentdisclosure is optimal operating point control. This feature allows aprime mover in the form of an internal combustion engine to operate atan optimal operating point (e.g., max efficiency, max power, min fuelconsumption, etc.), while varying wheel speeds and implement speeds inorder to be consistent with the operator's desired operation commandsand pre-defined optimal operating points for prime mover speed andimplement speed. In operation, a user provides input for speed andsteering of the vehicle, and the controller algorithm adjusts drivespeed controls, implement speed controls, etc., to maintain the engineat the optimal operating point. Engine control (fuel flow which drivesspeed, etc.) may be employed to enhance the system.

FIG. 16 illustrates a flow chart 500 for implementing optimal operationpoint control using the architecture of FIG. 13. When implementingoptimal operation pint control, wheel speed and/or implement speed arevaried to obtain the optimal prime mover speed. In certain instancesthis may lead to lower wheel speed and/or lower implement speed in orderto maintain the optimal prime mover speed.

Beginning at step 502 it is determined if optimal operating pointcontrol is enabled. Such determination can be based on operator inputvia, for example, a selector switch, pushbutton, operator interface orother input means operatively coupled to the controller 20. If optimaloperating point control is not enabled, then at block 504 normal controlis implemented and the process moves back to block 502. If at block 502optimal control is enabled, then at block 506 the optimal prime moverspeed is obtained.

The optimal prime mover speed (revolutions per minute) may be determinedbeforehand (e.g., in a laboratory or during design) and stored in memoryof the controller 20. The optimal operating speed may vary depending onambient conditions and/or system conditions. Thus, a plurality ofoptimal operating speeds may be stored in memory of the controller 20,such as in a lookup table or database along with corresponding ambientconditions and system conditions. Then, based on one or more ambientconditions (e.g., ambient air temperature, humidity, barometricpressure) and/or system conditions (e.g., prime mover temperature, oiltemperature, etc.) an optimal operating speed for the prime mover 56 canbe retrieved from memory of the controller 20. At block 508 the primemover 56 is operated at the optimal speed by providing a command to theprime mover speed control 210 and monitoring data provided by the primemover speed sensor 202.

Next at block 510 the desired vehicle speed and/or steering commands aredetermined, for example, from the user controls 18. For example, if thespeed input is displaced 50% of its maximum value, then the requestedspeed can be inferred to be 50% of rated speed.

Since optimal speed for the prime mover 56 may be less than its maximumspeed, in order for the implement speed and wheel speed to achieve theirrated speeds it may be necessary to alter a gear ratio between the primemover 56 and the implement 208 and a gear ratio between the prime mover56 and the hydrostatic transmission 52 and/or wheels 20. For example, ifthe prime mover has a maximum speed of 3600 RPM and a 1:1 gear ratiobetween the prime mover 56 and the implement 208 provides optimumimplement speed at the maximum prime mover speed, then if the optimalprime mover speed for the specific ambient and/or system condition isdetermined to be 2500 RPM, at block 512 the implement speed controller214 would change the drive ratio between the prime mover 56 and theimplement 208 (e.g., to 1.44:1).

Similarly, at block 514 if the vehicle rated speed is 10 MPH while theprime mover is operating at maximum speed (e.g., 3600 RPM) with a 20:1gear ratio between the prime mover and the wheels, then the optimal 2500RPM prime mover speed will prevent the vehicle from reaching the ratedspeed. In order to overcome this barrier, the gear ratio between theprime mover and the transmission and/or wheels can be changed to 15:1.Such gear ratio changes between the prime mover/implement and betweenthe prime mover/transmission/wheels may be implemented, for example,using a CVT.

Another feature that may be implemented in accordance with the presentdisclosure is four-wheel steering, without the need for complicatedmechanical linkages which often deliver less than optimal performancedue to wear, free play, and non-linear effects of tolerance stackups. Onvehicles that commonly employ two castering wheels and steer by means ofthe relative speed of the drive wheels, this type of system eliminatesthe issues associated with castering wheels that offer no lateralrestraining forces.

In accordance with the present embodiment, an operator provides inputfor the desired steering operation and the controller algorithm adjuststhe speed of each wheel and the steering attitude of the steerablewheels to produce the desired steering operations. In this embodimenteach steerable wheel's attitude is monitored and controlledindividually.

Referring to FIG. 17, a block diagram is provided that illustrates anexemplary architecture 300 for implementing four-wheel steering controlof a vehicle in accordance with the present disclosure. The vehicleimplementing the architecture of FIG. 17 includes non-driven frontsteering wheels and driven rear wheels (e.g., via independenthydrostatic transmissions). The architecture of FIG. 17 includes a primemover 56, such as an internal combustion engine, electric motor, or thelike, mechanically coupled to left and right transmissions, such ashydrostatic transmissions 52 l and 52 l coupled to a left and rightwheel, respectively (not shown). More specifically, an output shaft ofthe prime mover 56 may be coupled to an input shaft of left and rightfluid pumps as described herein. The left transmission 52 l controls thedelivery of power to the left wheel while the right transmission 52 rcontrols delivery of power to the right wheel.

The controller 20 is operatively coupled to the left and right pumps soas to control power output by the hydrostatic transmissions 52 l and 52r. For example, and as described herein, the controller 20 isoperatively coupled to a fluid power control device 72 l or 74 l toselectively control the delivery of fluid power to a left swashplate 64l of the left fluid pump 54 l. A similar configuration is provided forthe right fluid pump 54 r. In this manner, the controller 20 can controlpower output by the left and right transmissions 52 l and 52 rindependent of user input. Additionally, the position of the left andright swashplates 64 l and 64 r may be communicated to the controllervia left and right angle sensors 66 l and 66 r as described herein.Based on the detected swashplate position, the controller 20 can adjustthe fluid power provided to the respective swashplate.

Operator controls 18, such as speed controls, steering controls, etc.,can be provided to the controller 20. The controller 20, for example,based on operator input via the operator controls, can command theswashplates 64 l and 64 r to provide a desired power output from thehydrostatic transmissions 52 l and 52 r, as described in more detailwith respect to FIG. 19.

One or more steerable wheels 602 are coupled to a mechanical steeringsystem 604. The mechanical steering system 604 may comprise, forexample, an electric or hydraulic-assist unit coupled to associatedlinkage operative to turn the one or more wheels about an axis. Asteering actuator 606 delivers power to the assist unit based oncommands from the controller 20. A steering attitude sensor 608 iscoupled to the steering system 604 and detects the attitude of the oneor more wheels relative to a predetermined value and communicates theattitude to the controller 20. The attitude sensor may be coupled to thesteering system 604 or directly coupled to a respective steerable wheel602.

In the architecture of FIG. 17 where the rear wheels provide drive powerand steering, while the front wheels provide steering (i.e., no power).Steering is effected by creating a speed differential between the drivenwheels, and rotating the one or more steerable wheels about an axis.

All wheel or four wheel drive could be accomplished by adding individualdrives to the steerable wheels and providing control in a manner similarto that performed with the main drives. Drive power could be electric,hydraulic, pneumatic, etc.

FIG. 18 is a block diagram illustrating an alternative architecture 600′for implementing four-wheel steering control of a vehicle in accordancewith the present disclosure. The architecture 600′ is similar to that ofFIG. 17, but instead of including mechanical steering linkage coupled toone or more wheels, the architecture of FIG. 18 can utilize individualsteering actuators for each steerable wheel. A left wheel 602 l iscoupled to a left steering actuator 506 l, which in turn is coupled tothe controller 20. A left steering attitude sensor 608 l is coupled tothe left steerable wheel 602 l and provides wheel attitude to thecontroller 20. A similar arrangement is provided to a right wheel 602 r,where a right steering actuator 606 r is coupled to the right steerablewheel 602 l and receives commands from controller 20, and a rightsteering attitude sensor 608 r is coupled to the right wheel 602 r andprovides the wheel attitude to the controller 20.

Referring now to FIG. 19, illustrated is a flow chart 650 for performingfour-wheel steering in accordance with an aspect of the disclosure.Beginning at block 652, a desired turning direction for the vehicle isdetermined. The turning direction can be determined based on acomparison of the wheels coupled to each hydrostatic transmission. Forexample, if the driven wheels are rotating at the same speed, then itcan be presumed that the vehicle is to travel in a straight line.However, if one wheel is rotating faster than the other, it can beconcluded that a turn is being performed (e.g., if the right wheel isturning faster than the left wheel, then it can be concluded that a leftturn is being performed. Based on the differential between drivenwheels, the desired turn radius can be calculated. Alternatively,steering direction may be determined based on user input, e.g., based ona steering wheel or other steering input means that communicates thedesired steering radius to the controller.

At block 654, the obtained steering direction is analyzed to determineif the vehicle is to turn left, right or remain straight. If the vehicleis to remain straight (i.e., no turn is being performed), then at block656 the driven wheels are provided with the same speed command and thesteerable wheels are controlled to forward (straight) position. If thevehicle is to turn left, then at block 660 the left wheel is commandedto rotate slower than the right wheel, and at block 662 the steerablewheels are controlled to the left position. Finally, if the vehicle isto turn right, then at block 664 the right wheel is commanded to rotateslower than the left wheel, and at block 666 the steerable wheels arecontrolled to the right position.

Although the invention has been shown and described with respect to acertain embodiment or embodiments, it is obvious that equivalentalterations and modifications will occur to others skilled in the artupon the reading and understanding of this specification and the annexeddrawings. In particular regard to the various functions performed by theabove described elements (components, assemblies, devices, compositions,etc.), the terms (including a reference to a “means”) used to describesuch elements are intended to correspond, unless otherwise indicated, toany element which performs the specified function of the describedelement (i.e., that is functionally equivalent), even though notstructurally equivalent to the disclosed structure which performs thefunction in the herein illustrated exemplary embodiment or embodimentsof the invention. In addition, while a particular feature of theinvention may have been described above with respect to only one or moreof several illustrated embodiments, such feature may be combined withone or more other features of the other embodiments, as may be desiredand advantageous for any given or particular application.

1. A vehicle, comprising: a pump including a swashplate tiltable about aswashplate tilt axis, wherein rotation of the swashplate changes thetitle angle and effects a change in volumetric displacement of the pump;a controller operatively coupled to the swashplate to effect rotation ofthe swashplate, the controller including a processor and memory; andlogic stored in the memory and executable by the processor, the logicconfigured to automatically control at least one vehicle characteristicindependent of a user input command.
 2. The vehicle according to claim1, wherein the controller is configured to effect rotation of theswashplate through application of fluid power to the swashplate.
 3. Thevehicle according to claim 1, wherein the logic configured toautomatically control at least one vehicle characteristic independent ofa user input command includes logic configured to effect rotation of theswashplate independent of the user input command.
 4. The vehicleaccording to claim 1, further comprising a prime mover for providingpower to the vehicle, wherein the logic configured to automaticallycontrol at least one vehicle characteristic independent of a user inputcommand includes: logic configured to determine an optimal operatingspeed for the prime mover based on at least one system condition orambient condition; and logic configured to regulate the prime moverspeed at the optimal operating speed.
 5. The vehicle according to claim4, further comprising: an implement drivingly coupled to the primemover; a plurality of wheels drivingly coupled to the prime mover; andlogic configured to alter a drive ratio between the implement and theprime mover so as to maintain the implement speed at a first prescribedspeed, or alter a drive ratio between the prime mover and the pluralityof wheels so as to maintain the wheel speed about a second prescribedlevel.
 6. The vehicle according to claim 1, wherein the logic configuredto automatically control at least one vehicle characteristic independentof a user input command includes logic configured to automaticallycontrol a wheel speed of the vehicle independent of the user inputcommand.
 7. The vehicle according to claim 1, comprising: at least oneimplement, wherein the controller is operatively coupled to the at leastone implement; and wherein the configured to automatically control atleast one vehicle characteristic independent of the user input commandincludes logic configured to regulate, independent of the user inputcommand, a speed of the at least one implement at a prescribed speed. 8.The vehicle according to claim 7, wherein the at least one implementcomprises mower blades.
 9. The vehicle according to claim 7, furthercomprising a prime mover drivingly coupled to the at least oneimplement, wherein the logic configured to regulate a speed of the atleast one implement includes logic configured to vary a speed of theprime mover to regulate the implement speed at the prescribed speed. 10.The vehicle according to claim 9, further comprising a prime mover speedsensor operatively coupled to the prime mover, wherein the logicconfigured to vary a speed of the prime mover includes logic configuredto use data from the prime mover speed sensor to vary the speed of theprime mover.
 11. The vehicle according to claim 7, further comprising aprime mover drivingly coupled to the at least one implement, wherein thelogic configured to regulate a speed of the at least one implementincludes logic configured to vary a drive ratio between the prime moverand the at least one implement to maintain the implement speed at theprescribed speed.
 12. The vehicle according to claim 11, furthercomprising a speed sensor operatively coupled to the at least oneimplement, wherein the logic configured to vary a drive ratio includeslogic configured to use data from the implement speed sensor to controlthe drive ratio.
 13. The vehicle according to claim 1, furthercomprising logic configured to alter resolution of a speed input commandbased on an operating mode of the vehicle.
 14. The vehicle according toclaim 13, wherein the logic configured to alter resolution of a speedinput command based on an operating mode of the vehicle include logicconfigured to increase a maximum speed of the vehicle and decrease asensitivity of a speed control input when in a first mode, and decreasea maximum speed of the vehicle and increase the sensitivity of the speedinput command when in a second mode.
 15. The vehicle according to claim1, further comprising: a first driven wheel arranged on a first side ofthe vehicle; a second driven wheel arranged on a second side of thevehicle; at least one steerable wheel; at least one steering attitudesensor coupled to the at least one steerable wheel and to thecontroller, the attitude sensor operative to communicate a steeringattitude of the at least one wheel to the controller; and at least onesteering actuator operatively coupled to the at least one steerablewheel and to the controller, wherein the logic configured toautomatically control at least one vehicle characteristic independent ofa user input command includes logic configured to command the at leastone steering actuator to turn the at least one steerable wheel based ona speed differential between the at least two driven wheels and dataprovided by the steering attitude sensor.
 16. The vehicle according toclaim 15, wherein the at least one steerable wheel comprises a pluralityof steerable wheels, each wheel operatively coupled to a respectivesteering actuator and attitude sensor.
 17. The vehicle according toclaim 1, further comprising a hydrostatic transmission.
 18. A vehiclecontroller for operating a vehicle including a pump having a swashplatetiltable about a swashplate tilt axis, wherein rotation of theswashplate changes the title angle and effects a change in volumetricdisplacement of the pump, the controller comprising: a processor andmemory; and logic stored in the memory and executable by the processor,the logic configured to effect rotation of the swashplate independent ofa user input command.
 19. The controller according to claim 18, furthercomprising logic configured to automatically control at least onevehicle characteristic independent of a user input command.
 20. Thecontroller according to claim 19, further comprising: logic configuredto determine an optimal operating speed for a prime mover based on atleast one system condition or ambient condition; and logic configured toregulate a prime mover speed at the optimal operating speed.
 21. Thecontroller according to claim 19, wherein the logic configured toautomatically control at least one vehicle characteristic independent ofa user input command includes logic configured to automatically controla wheel speed of the vehicle independent of the user input command. 22.The controller according to claim 19, further comprising logicconfigured to regulate, independent of a user input command, a speed ofat least one implement at a prescribed speed.
 23. The controlleraccording to claim 18, further comprising logic configured to alterresolution of a speed input command based on an operating mode of thevehicle.
 24. The controller according to claim 18, wherein the logicconfigured to automatically control at least one vehicle characteristicindependent of a user input command includes logic configured to commandat least one steering actuator to turn at least one steerable wheelbased on a speed differential between at least two driven wheels anddata provided by a steering attitude sensor.